Quantification of Alzheimer Amyloid β Peptides Ending at Residues 40 and 42 by Novel ELISA Systems

Non-linear transformation of enzyme-linked immunosorbent assay (ELISA) measurements allows usage of linear models for data analysis

Background

In research questions such as in resistance breeding against the Beet necrotic yellow vein virus it is of interest to compare the virus concentrations of samples from different groups. The enzyme-linked immunosorbent assay (ELISA) counts as the standard tool to measure virus concentrations. Simple methods for data analysis such as analysis of variance (ANOVA), however, are impaired due to non-normality of the resulting optical density (OD) values as well as unequal variances in different groups.

Methods

To understand the relationship between the OD values from an ELISA test and the virus concentration per sample, we used a large serial dilution and modelled its non-linear form using a five parameter logistic regression model. Furthermore, we examined if the quality of the model can be increased if one or several of the model parameters are defined beforehand. Subsequently, we used the inverse of the best model to estimate the virus concentration for every measured OD value.

Results

We show that the transformed data are essentially normally distributed but provide unequal variances per group. Thus, we propose a generalised least squares model which allows for unequal variances of the groups to analyse the transformed data.

Conclusions

ANOVA requires normally distributed data as well as equal variances. Both requirements are not met with raw OD values from an ELISA test. A transformation with an inverse logistic function, however, gives the possibility to use linear models for data analysis of virus concentrations. We conclude that this method can be applied in every trial where virus concentrations of samples from different groups are to be compared via OD values from an ELISA test. To encourage researchers to use this method in their studies, we provide an R script for data transformation as well as the data from our trial.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-022-01804-3.

Detection of osteoarthritis in dogs by metabolic, pro-inflammatory and degenerative synovial fluid biomarkers and traditional radiographic screening: A pilot study

Secondary osteoarthritis (OA) is a slow progressive, common disorder of synovial joints in dogs. It is characterized by a loss of balance between the synthesis and degeneration of articular cartilage components. Its diagnosis is currently based on the presence of clear radiographic changes, which only occur in the later stages of the disease. Hence, early diagnosis of OA remains a major problem. Therefore, interest in synovial fluid (SF) biomarkers has emerged. Besides pro-inflammatory and degenerative markers, i.e. tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), tenascin-c (TN-C) and matrix metalloproteinase-2 (MMP-2), metabolic parameters, i.e. pH, glucose and lactate, can potentially be used to detect OA. The current study demonstrated statistically significant differences in the SF levels of pH, glucose and lactate between OA-affected and normal joints. In addition, the in-house validated immuno-assays for TNF-alpha, IL-1beta, TN-C and MMP-2 allowed to demonstrate also statistically significant differences in the SF concentrations for all these biomarkers - except TNF-alpha - between OA-affected and normal joints. However, no correlation was found between any of these biomarkers and the currently used radiographic scoring system for OA in dogs. Future research is warranted to explore the potential of these biomarkers in the early detection of OA and in the severity characterization of this disease.

New Insights into the Spontaneous Human Alzheimer's Disease-Like Model Octodon degus: Unraveling Amyloid-β Peptide Aggregation and Age-Related Amyloid Pathology

Alzheimer's disease (AD) is the most common cause of dementia worldwide. Despite advances in our understanding of the molecular milieu driving AD pathophysiology, no effective therapy is currently available. Moreover, various clinical trials have continued to fail, suggesting that our approach to AD must be revised. Accordingly, the development and validation of new models are highly desirable. Over the last decade, we have been working with Octodon degus (degu), a Chilean rodent, which spontaneously develops AD-like neuropathology, including increased amyloid-β (Aβ) aggregates, tau hyperphosphorylation, and postsynaptic dysfunction. However, for proper validation of degu as an AD model, the aggregation properties of its Aβ peptide must be analyzed. Thus, in this study, we examined the capacity of the degu Aβ peptide to aggregate in vitro. Then, we analyzed the age-dependent variation in soluble Aβ levels in the hippocampus and cortex of third- to fifth-generation captive-born degu. We also assessed the appearance and spatial distribution of amyloid plaques in O. degus and compared them with the plaques in two AD transgenic mouse models. In agreement with our previous studies, degu Aβ was able to aggregate, forming fibrillar species in vitro. Furthermore, amyloid plaques appeared in the anterior brain structures of O. degus at approximately 32 months of age and in the whole brain at 56 months, along with concomitant increases in Aβ levels and the Aβ42/Aβ40 ratio, indicating that O. degus spontaneously develops AD-like pathology earlier than other spontaneous models. Based on these results, we can confirm that O. degus constitutes a valuable model to improve AD research.

A highly sensitive plasma-based amyloid-β detection system through medium-changing and noise cancellation system for early diagnosis of the Alzheimer's disease

We developed an interdigitated microelectrode (IME) sensor system for blood-based Alzheimer's disease (AD) diagnosis based on impedimetric detection of amyloid-β (Aβ) protein, which is a representative candidate biomarker for AD. The IME sensing device was fabricated using a surface micromachining process. For highly sensitive detection of several tens to hundreds of picogram/mL of Aβ in blood, medium change from plasma to PBS buffer was utilized with signal cancellation and amplification processing (SCAP) system. The system demonstrated approximately 100-folds higher sensitivity according to the concentrations. A robust antibody-immobilization process was used for stability during medium change. Selectivity of the reaction due to the affinity of Aβ to the antibody and the sensitivity according to the concentration of Aβ were also demonstrated. Considering these basic characteristics of the IME sensor system, the medium change was optimized in relation to the absolute value of impedance change and differentiated impedance changes for real plasma based Aβ detection. Finally, the detection of Aβ levels in transgenic and wild-type mouse plasma samples was accomplished with the designed sensor system and the medium-changing method. The results confirmed the potential of this system to discriminate between patients and healthy controls, which would enable blood-based AD diagnosis.

Plant-Derived Chimeric Virus Particles for the Diagnosis of Primary Sjögren Syndrome

Plants are ideal for the production of protein-based nanomaterials because they synthesize and assemble complex multimeric proteins that cannot be expressed efficiently using other platforms. Plant viruses can be thought of as self-replicating proteinaceous nanomaterials generally stable and easily produced in high titers. We used Potato virus X (PVX), chimeric virus particles, and Cowpea mosaic virus, empty virus-like particles to display a linear peptide (lipo) derived from human lipocalin, which is immunodominant in Sjögren's syndrome (SjS) and is thus recognized by autoantibodies in SjS patient serum. These virus-derived nanoparticles were thus used to develop a diagnostic assay for SjS based on a direct enzyme linked immunosorbent assay format. We found that PVX-lipo formulations were more sensitive than the chemically synthesized immunodominant peptide and equally specific when used to distinguish between healthy individuals and SjS patients. Our novel assay therefore allows the diagnosis of SjS using a simple, low-invasive serum test, contrasting with the invasive labial biopsy required for current tests. Our results demonstrate that nanomaterials based on plant viruses can be used as diagnostic reagents for SjS, and could also be developed for the diagnosis of other diseases.

Technical performance of a novel, fully automated electrochemiluminescence immunoassay for the quantitation of β-amyloid (1-42) in human cerebrospinal fluid

INTRODUCTION

Available assays for quantitation of the Alzheimer's disease (AD) biomarker amyloid-beta 1-42 (Aβ [1-42]) in cerebrospinal fluid demonstrate significant variability and lack of standardization to reference measurement procedures (RMPs). We report analytical performance data for the novel Elecsys β-amyloid (1-42) assay (Roche Diagnostics).

METHODS

Lot-to-lot comparability was tested using method comparison. Performance parameters were measured according to Clinical & Laboratory Standards Institute (CLSI) guidelines. The assay was standardized to a Joint Committee for Traceability in Laboratory Medicine (JCTLM) approved RMP.

RESULTS

Limit of quantitation was <11.28 pg/mL, and the assay was linear throughout the measuring range (200-1700 pg/mL). Excellent lot-to-lot comparability was observed (correlation coefficients [Pearson's r] >0.995; bias in medical decision area <2%). Repeatability coefficients of variation (CVs) were 1.0%-1.6%, intermediate CVs were 1.9%-4.0%, and intermodule CVs were 1.1%-3.9%. Estimated total reproducibility was 2.0%-5.1%. Correlation with the RMP was good (Pearson's r, 0.93).

DISCUSSION

The Elecsys β-amyloid (1-42) assay has high analytical performance that may improve biomarker-based AD diagnosis.

Aβ42 and Aβ40: similarities and differences

The abnormal accumulation of amyloid-β (Aβ) peptide in the brain is one of the most important hallmarks of Alzheimer's disease. Aβ is an aggregation-prone and toxic polypeptide with 39-43 residues, derived from the amyloid precursor protein proteolysis process. According to the amyloid hypothesis, abnormal accumulation of Aβ in the brain is the primary influence driving Alzheimer's disease pathologies. Among all kinds of Aβ isoforms, Aβ40 and Aβ42 are believed to be the most important ones. Although these two kinds of Aβ differ only in two amino acid residues, recent studies show that they differ significantly in their metabolism, physiological functions, toxicities, and aggregation mechanism. In this review, we mainly summarize the similarities and differences between Aβ42 and Aβ40, recent studies on selective inhibitors as well as probes will also be mentioned.

Stability and Reproducibility Underscore Utility of RT-QuIC for Diagnosis of Creutzfeldt-Jakob Disease

Real-time quaking-induced conversion (RT-QuIC) allows the amplification of miniscule amounts of scrapie prion protein (PrP^Sc). Recent studies applied the RT-QuIC methodology to cerebrospinal fluid (CSF) for diagnosing human prion diseases. However, to date, there has not been a formal multi-centre assessment of the reproducibility, validity and stability of RT-QuIC in this context, an indispensable step for establishment as a diagnostic test in clinical practice. In the present study, we analysed CSF from 110 prion disease patients and 400 control patients using the RT-QuIC method under various conditions. In addition, “blinded” ring trials between different participating sites were performed to estimate reproducibility. Using the previously established cut-off of 10,000 relative fluorescence units (rfu), we obtained a sensitivity of 85 % and a specificity of 99 %. The multi-centre inter-laboratory reproducibility of RT-QuIC revealed a Fleiss’ kappa value of 0.83 (95 % CI: 0.40–1.00) indicating an almost perfect agreement. Moreover, we investigated the impact of short-term CSF storage at different temperatures, long-term storage, repeated freezing and thawing cycles and the contamination of CSF with blood on the RT-QuIC seeding response. Our data indicated that the PrP^Sc seed in CSF is stable to any type of storage condition but sensitive to contaminations with blood (>1250 erythrocytes/μL), which results in a false negative RT-QuIC response. Fresh blood-contaminated samples (3 days) can be rescued by removal of erythrocytes. The present study underlines the reproducibility and high stability of RT-QuIC across various CSF storage conditions with a remarkable sensitivity and specificity, suggesting RT-QuIC as an innovative and robust diagnostic method.

Andrographolide reduces cognitive impairment in young and mature AβPPswe/PS-1 mice

Alzheimer’s disease (AD) is a neurodegenerative disorder in which the amyloid-β (Aβ) oligomers are a key factor in synaptic impairment and in spatial memory decline associated with neuronal dysfunction. This impairment includes synaptic failure associated with the loss of synaptic proteins that contribute to AD progression. Interestingly, the use of natural compounds is an emergent conceptual strategy in the search for drugs with therapeutic potentials for treating neurodegenerative disorders. In the present study, we report that andrographolide (ANDRO), which is a labdane diterpene extracted from Andrographis paniculata, increases slope of field excitatory postsynaptic potentials (fEPSP) in the CA1 region of hippocampal slices and inhibits long-term depression (LTD), protecting the long-term potentiation (LTP) against the damage induced by Aβ oligomers in vitro, most likely by inhibiting glycogen synthase kinase-3β (GSK-3β). Additionally, ANDRO prevents changes in neuropathology in two different age groups (7- and 12-month-old mice) of an AβPPswe/PS-1 Alzheimer’s model. ANDRO reduces the Aβ levels, changing the ontogeny of amyloid plaques in hippocampi and cortices in 7-month-old mice, and reduces tau phosphorylation around the Aβ oligomeric species in both age groups. Additionally, we observed that ANDRO recovers spatial memory functions that correlate with protecting synaptic plasticity and synaptic proteins in two different age groups. Our results suggest that ANDRO could be used in a potential preventive therapy during AD progression.

The role of flotillins in regulating aβ production, investigated using flotillin 1-/-, flotillin 2-/- double knockout mice

Flotillin 1 and flotillin 2 associate in the plasma membrane to form microdomains that have roles in cell signaling, regulation of cell-cell contacts, membrane-cytoskeletal interactions, and endocytosis. They are thought to be involved in the trafficking and hence processing of the Amyloid Precursor Protein, APP. In this study we set out to obtain in vivo confirmation of a link between flotillins and cleavage of APP to release amyloidogenic Aβ peptide, and to generate tools that would allow us to ask whether flotillins are functionally redundant. We used a mouse model for Aβ-dependent cerebral amyloidosis, APPPS1 mice, combined with deletion of either flotillin 1 singly, or flotillin 1 and flotillin 2 together. There was a small but significant reduction in Aβ levels, and the abundance of congo-red stained plaques, in brains of 12 week old mice lacking flotillin 1. A similar reduction in Aβ levels was observed in the flotillin 1-/-, flotillin 2-/- double knockouts. We did not observe large effects on the clustering or endocytosis of APP in flotillin 1-/- mouse embryonic fibroblasts. We conclude that flotillins are likely to play some role in APP trafficking or processing, but the relevant cellular mechanisms require more investigation. The availability of flotillin 1-/-, flotillin 2-/- mice, which have no overt phenotypes, will facilitate research into flotillin function in vivo.

hESC-secreted proteins can be enriched for multiple regenerative therapies by heparin-binding

This work builds upon our findings that proteins secreted by hESCs exhibit pro-regenerative activity, and determines that hESC-conditioned medium robustly enhances the proliferation of both muscle and neural progenitor cells. Importantly, this work establishes that it is the proteins that bind heparin which are responsible for the pro-myogenic effects of hESC-conditioned medium, and indicates that this strategy is suitable for enriching the potentially therapeutic factors. Additionally, this work shows that hESC-secreted proteins act independently of the mitogen FGF-2, and suggests that FGF-2 is unlikely to be a pro-aging molecule in the physiological decline of old muscle repair. Moreover, hESC-secreted factors improve the viability of human cortical neurons in an Alzheimer's disease (AD) model, suggesting that these factors can enhance the maintenance and regeneration of multiple tissues in the aging body.

Pre-analytical factors influencing the stability of cerebrospinal fluid proteins

Cerebrospinal fluid (CSF) is a potential source for new biomarkers due to its proximity to the brain. This study aimed to clarify the stability of the CSF proteome when undergoing pre-analytical factors. We investigated the effects of repeated freeze/thaw cycles, protease inhibitors and delayed storage for 4h, 24h or 14 days at -20°C, 4°C and room temperature (RT) after centrifugation compared with our standard practice of two hours at RT before placing the samples in an -80°C environment. The results were obtained using immunoassays for amyloid-beta 1-42 (Aβ42), tau, phosphorylated tau (P-tau) and cystatin C and using surface-enhanced laser desorption/ionisation time-of-flight (SELDI-TOF) mass spectrometry for proteomic profiling. Tau and P-tau were susceptible to repeated freeze/thaw cycles while SELDI-TOF analysis produced eight significant peaks and additional artefact peaks from samples with added protease inhibitors. Delayed storage for different durations and in different temperatures produced six significant SELDI-TOF peaks. Aβ42 and tau were susceptible to increased temperatures and the duration before storage, whereas P-tau and cystatin C were not. Transthyretin and several of its isoforms were found using SELDI-TOF and were susceptible to freeze/thaw cycles and to increased temperature and length of time prior to storage. We recommend that CSF should be collected and centrifuged immediately after sampling and prior to storage at -80°C without the addition of protease inhibitors. Freeze/thawing should be avoided because of the instability of tau, P-tau and transthyretin. Standardised CSF sampling, handling and storage for biomarker research are essential for accurately comparing the results obtained by different studies and institutions.

Neurochemical dementia diagnostics in Alzheimer's disease: where are we now and where are we going?

Neurochemical dementia diagnostics (NDD) is a routine laboratory tool used in the diagnostic process for patients with neurodegenerative disorders, such as Alzheimer's disease. Currently, two groups of biomarkers analyzed in the cerebrospinal fluid are considered - namely amyloid-β peptides and Tau proteins - along with the hyperphosphorylated forms of the latter (pTau). Current directions in the development of NDD include the following: search for novel biomarkers with improved analytical or diagnostic performance; optimization of the analysis of the biomarkers already available (e.g., by improved quality control and interlaboratory comparison of results); applications of novel technologies enabling better management of patient samples; and search for biomarkers in the blood. This article presents the state-of-the-art in the field of cerebrospinal fluid-based NDD, and also summarizes some of the hypotheses of how the future development of NDD tools might look.

Proteasome inhibition leads to early loss of synaptic proteins in neuronal culture

A dysfunctional ubiquitin proteasome system may be a mediating factor of disease progression in Lewy body dementia (LBD). The effects of proteasome inhibition using lactacystin and epoxomicin in primary neuronal culture were studied to assess the validity of this model to reflect the cortical pathology of LBD. Treatment of primary cortical neurons with 5 μM lactacystin for 24 h led to a 38 % reduction in the levels of β-III-tubulin (p < 0.05), a 48 % reduction in the levels of synaptophysin (p < 0.05) and a 74 % reduction in the levels of drebrin (p < 0.01), when compared to controls. Results for epoxomicin were similar. The loss of neuronal protein occurred prior to any loss of mitochondrial activity or cell death. The results are reflective of the loss of synapses and the synaptic changes observed in LBD, which may be an early event in the neurodegeneration of LBD. The similarities with the pathological changes in LBD highlight the possibility that this model can potentially provide a platform to test novel treatments.

Antipsychotic medication is associated with selective alterations in ventricular cerebrospinal fluid Aβ 40 and tau in patients with intractable unipolar depression

OBJECTIVE

Alterations in plasma and in lumbar cerebrospinal fluid amyloid-B peptide (Aβ) levels have been reported in Alzheimer's disease. Studies have also suggested similar changes in depressed patients. No information is available on the impact of psychotropic drugs on this in patients with depression. We therefore quantified Aβ in ventricular cerebrospinal fluid (CSF) in a population of patients with treatment-resistant depression, with and without antipsychotic medication.

METHOD

A cross-sectional study of 32 patients undergoing subcaudate tractotomy for major (unipolar) depressive disorder. Ventricular CSF concentrations of Aβ peptide 1-40 and 1-42, also p-tau and total tau were determined by Western blotting or enzyme-linked immunosorbent assay.

RESULTS

Patients taking antipsychotic medication in the 2 weeks prior to surgery demonstrated significantly higher levels of Aβ 1-40 (mean ± SD: 727.3 ± 382.3 vs. 440.9 ± 337.2 pg/ml; p = 0.032, Student's t-test) but unaltered Aβ 1-42 (mean 72.1 ± 67.5 vs. 60.0 ± 56.7 pg/ml; p = 0.587) compared to a matched sample not treated with antipsychotic drugs. The same group demonstrated elevated total tau (mean 945.0 ± 422.2 vs. 534.3 ± 388.3 pg/ml; p = 0.010) but not p-tau (mean 98.6 ± 71.5 vs. 88.1 ± 70.5 pg/ml; p = 0.694). No similar effect was found with lithium, antidepressants, carbamazepine or benzodiazepines.

CONCLUSIONS

This preliminary study suggests antipsychotic drugs, widely used in patients with severe depression across all age ranges, may be associated with alteration of Aβ 1-40 and total tau, indices strongly linked with progressive organic brain disease. Further confirmatory work is needed.

Single-channel Ca(2+) imaging implicates Aβ1-42 amyloid pores in Alzheimer's disease pathology

High-resolution imaging of calcium influx reveals that the Aβ peptides implicated in Alzheimer’s disease form highly toxic Ca²⁺-permeable pores.

Oligomeric forms of Aβ peptides are implicated in Alzheimer’s disease (AD) and disrupt membrane integrity, leading to cytosolic calcium (Ca²⁺) elevation. Proposed mechanisms by which Aβ mediates its effects include lipid destabilization, activation of native membrane channels, and aggregation of Aβ into Ca²⁺-permeable pores. We distinguished between these using total internal reflection fluorescence (TIRF) microscopy to image Ca²⁺ influx in Xenopus laevis oocytes. Aβ1–42 oligomers evoked single-channel Ca²⁺ fluorescence transients (SCCaFTs), which resembled those from classical ion channels but which were not attributable to endogenous oocyte channels. SCCaFTs displayed widely variable open probabilities (P_o) and stepwise transitions among multiple amplitude levels reminiscent of subconductance levels of ion channels. The proportion of high P_o, large amplitude SCCaFTs grew with time, suggesting that continued oligomer aggregation results in the formation of highly toxic pores. We conclude that formation of intrinsic Ca²⁺-permeable membrane pores is a major pathological mechanism in AD and introduce TIRF imaging for massively parallel single-channel studies of the incorporation, assembly, and properties of amyloidogenic oligomers.

A monoclonal antibody against synthetic Aβ dimer assemblies neutralizes brain-derived synaptic plasticity-disrupting Aβ

Diverse lines of evidence indicate that pre-fibrillar, diffusible assemblies of the amyloid β-protein (Aβ) play an important role in Alzheimer's disease pathogenesis. Although the precise molecular identity of these soluble toxins remains unsettled, recent experiments suggest that sodium dodecyl sulfate (SDS)-stable Aβ dimers may be the basic building blocks of Alzheimer's disease-associated synaptotoxic assemblies and as such present an attractive target for therapeutic intervention. In the absence of sufficient amounts of highly pure cerebral Aβ dimers, we have used synthetic disulfide cross-linked dimers (free of Aβ monomer or fibrils) to generate conformation-specific monoclonal antibodies. These dimers aggregate to form kinetically trapped protofibrils, but do not readily form fibrils. We identified two antibodies, 3C6 and 4B5, which preferentially bind assemblies formed from covalent Aβ dimers, but do not bind to Aβ monomer, amyloid precursor protein, or aggregates formed by other amyloidogenic proteins. Monoclonal antibody 3C6, but not an IgM isotype-matched control antibody, ameliorated the plasticity-disrupting effects of Aβ extracted from the aqueous phase of Alzheimer's disease brain, thus suggesting that 3C6 targets pathogenically relevant Aβ assemblies. These data prove the usefulness of covalent dimers and their assemblies as immunogens and recommend further investigation of the therapeutic and diagnostic utility of monoclonal antibodies raised to such assemblies.

Detrimental effects of arachidonic acid and its metabolites in cellular and mouse models of Alzheimer's disease: structural insight

Inflammation is believed to be integral to the pathogenesis of Alzheimer's disease (AD). Arachidonic acid (AA) is the most important omega-6 fatty acid and a mediator of inflammatory pathways. High-sensitivity enzyme linked immunosorbent assay shows that AA and its various metabolites; prostaglandins, thromboxanes, and leukotriene B4 resulted in significantly higher secretion of both Abeta40 and 42 peptides. A combination of identical number of alternate cis and trans double bonds either at positions Δ5 or 7Z,13 or 15E (such as PGE(2), PGF(2α), THXB2 and PGF(2α)EA) or at positions Δ6Z,8E,10E,14Z (such as LB4) built in the 3-dimensional structure of 20-carbon fatty acyl chains believed to be responsible for their detrimental action. CP 24,879 and sesamin, 2 inhibitors of the AA pathway suppressed the production of amyloid-beta (Aβ) peptides. Immunoblotting experiments and use of SP-C99 transfected COS-7 cells suggested that AA and its metabolites-driven altered production of Aβ is mediated through gamma-secretase cleavage of amyloid precursor protein (APP). An early-onset AD transgenic mouse model expressing the double-mutant form of human amyloid precursor protein, Swedish (K670N/M671L) and Indiana (V717F), corroborated our in vitro findings by showing higher levels of Abeta and amyloid plaques in the brains, when they were fed chow supplemented with 2% AA. Our work not only supports that AA and its metabolites are involved in the production of Aβ and in the pathogenesis of AD but also contributes to clarify aspects of structure-activity relationship helpful for future nonsteroidal anti-inflammatory drugs (NSAIDs) research.

Oleic acid ameliorates amyloidosis in cellular and mouse models of Alzheimer's disease

Several lines of evidence support protective as well as deleterious effects of oleic acid (OA) on Alzheimer's disease (AD) and other neurological disorders; however, the bases of these effects are unclear. Our investigation demonstrates that amyloid precursor protein (APP) 695 transfected Cos-7 cells supplemented with OA have reduced secreted amyloid-beta (Aβ) levels. An early-onset AD transgenic mouse model expressing the double-mutant form of human APP, Swedish (K670N/M671L) and Indiana (V717F), corroborated our in vitro findings when they were fed a high-protein, low-fat (18% reduction), cholesterol-free diet enriched with OA. These mice exhibited an increase in Aβ40/Aβ42 ratio, reduced levels of beta-site APP cleaving enzyme (BACE) and reduced presenilin levels along with reduced amyloid plaques in the brain. The decrease in BACE levels was accompanied by increased levels of a non-amyloidogenic soluble form of APP (sAPPα). Furthermore, the low-fat/+OA diet resulted in an augmentation of insulin-degrading enzyme and insulin-like growth factor-II. These results suggest that OA supplementation and cholesterol intake restriction in a mouse model of AD reduce AD-type neuropathology.

Structural insight into the differential effects of omega-3 and omega-6 fatty acids on the production of Abeta peptides and amyloid plaques

Several studies have shown the protective effects of dietary enrichment of various lipids in several late-onset animal models of Alzheimer Disease (AD); however, none of the studies has determined which structure within a lipid determines its detrimental or beneficial effects on AD. High-sensitivity enzyme-linked immunosorbent assay (ELISA) shows that saturated fatty acids (SFAs), upstream omega-3 FAs, and arachidonic acid (AA) resulted in significantly higher secretion of both Aβ 40 and 42 peptides compared with long chain downstream omega-3 and monounsaturated FAs (MUFA). Their distinct detrimental action is believed to be due to a structural template found in their fatty acyl chains that lack SFAs, upstream omega-3 FAs, and AA. Immunoblotting experiments and use of APP-C99-transfected COS-7 cells suggest that FA-driven altered production of Aβ is mediated through γ-secretase cleavage of APP. An early-onset AD transgenic mouse model expressing the double-mutant form of human amyloid precursor protein (APP); Swedish (K670N/M671L) and Indiana (V717F), corroborated in vitro findings by showing lower levels of Aβ and amyloid plaques in the brain, when they were fed a low fat diet enriched in DHA. Our work contributes to the clarification of aspects of structure-activity relationships.

Confounding factors influencing amyloid Beta concentration in cerebrospinal fluid

Background. Patients afflicted with Alzheimer's disease (AD) exhibit a decrease in the cerebrospinal fluid (CSF) concentration of the 42 amino acid form of β-amyloid (Aβ₄₂). However, a high discrepancy between different centers in measured Aβ₄₂ levels reduces the utility of this biomarker as a diagnostic tool and in monitoring the effect of disease modifying drugs. Preanalytical and analytical confounding factors were examined with respect to their effect on the measured Aβ₄₂ level. Methods. Aliquots of CSF samples were either treated differently prior to Aβ₄₂ measurement or analyzed using different commercially available xMAP or ELISA assays. Results. Confounding factors affecting CSF Aβ₄₂ levels were storage in different types of test tubes, dilution with detergent-containing buffer, plasma contamination, heat treatment, and the origin of the immunoassays used for quantification. Conclusion. In order to conduct multicenter studies, a standardized protocol to minimize preanalytical and analytical confounding factors is warranted.

Phospholipids and a phospholipid-rich diet alter the in vitro amyloid-beta peptide levels and amyloid-beta 42/40 ratios

Amyloid-beta peptides (Abeta) generated by proteolysis of the beta-amyloid precursor protein (APP) by beta- and gamma-secretases play an important role in the pathogenesis of Alzheimer's disease (AD). There is mounting evidence that the lipid matrix of neuronal cell membranes plays an important role in the accumulation of Abeta peptides into senile plaques, one of the hallmarks of AD. With the aim to clarify the molecular basis of the interaction between Abeta and cellular membranes, we investigated the effects of various phospholipids (PLs) and a PL-rich diet on Abeta production. Here we show that modulation of Abeta production and Abeta42:40 ratio is not limited to individual fatty acids, rather it is the composition of the PLs of the membrane bilayer, that influences the specificity and level of the regulated intramembranous proteolysis of APP by the gamma-secretase complex. We show that Abeta levels in the conditioned media, in response to some of the PL supplements, is increased in the center and decreased on either side of a graph that resembles bell-shaped distribution. This means that the PLs have less of a tendency to produce unusually extreme effects on Abeta production in SP-C99 transfected Cos-7 cultured cells. We proposed a mechanism-based hypothesis to rationalize PLs' effects on Abeta production.

A miniaturized 1536-well format gamma-secretase assay

gamma-Secretase is an aspartyl protease that cleaves multiple substrates including the amyloid precursor protein (APP) and the Notch proteins. Abnormal proteolysis of APP is involved in the pathogenesis of Alzheimer's disease (AD) and overactive Notch signaling plays an oncogenic role in a variety of cancers. gamma-Secretase has emerged as a promising target for drug development in the treatment of AD and cancer. Assays with increased capacity for high-throughput screening would allow for quicker screening of chemical libraries and facilitate inhibitor development. We have developed a homogeneous time-resolved fluorescence (HTRF)-based assay that makes use of a novel biotinylated recombinant APP substrate and solubilized membrane preparation as the source of the gamma-secretase enzyme. The assay was miniaturized to a 1536-well format and validated in a pilot screen against a library of approximately 3,000 compounds. The overall assay performance was robust due to a calculated Z' factor of 0.74 and its demonstrated ability to identify known gamma-secretase inhibitors such as pepstatin A. This validated assay can readily be used for primary screening against large chemical libraries searching for novel inhibitors of gamma-secretase activity that may represent potential therapeutics for AD and a variety of neoplasms.

Quantification of amyloid-beta 40 in cerebrospinal fluid

BACKGROUND

Truncated forms and full-length forms of the amyloid-beta 40 (Abeta40) are key molecules in the pathogenesis of dementia, and are detectable in CSF. Reliable methods to detect these biomarkers in CSF are of great importance for understanding the disease mechanisms and for diagnostic purposes.

METHODS

VU-alpha-Abeta40, a monoclonal antibody (mAb) specifically detecting Abeta40, was generated and characterized by solid and fluid phase ELISA, surface plasmon resonance spectroscopy (SPRS), immunoprecipitation (IP), immunohistochemical and Western blot (WB) analysis. In addition, an ELISA with VU-alpha-Abeta40 as catching and 6E10 as detecting mAbs was set up and validated. This ELISA was used to measure Abeta40 in CSF of controls (N=27), patients with Alzheimer's disease (AD; N=20), frontotemporal lobe dementia (FTLD; N=14), noninflammatory (N=15) and inflammatory (N=15) neurological conditions.

RESULTS

VU-alpha-Abeta40 specifically recognizes Abeta40 with high affinity (K(A)=1.3x10(9) M(-1)) and detects Abeta40 in AD brain specimens. The developed sandwich ELISA has a detection limit of 0.21 ng/mL, a mean recovery of 90%, and an intra- and inter-assay CV of 1.4% and 7.3%. FTLD patients had a lower mean level of Abeta40 (8.8 (1.9) ng/mL) than controls (12.0 (1.7) ng/mL); p<0.01).

CONCLUSIONS

VU-alpha-Abeta40 was successfully implemented in an ELISA which enables us to measure Abeta40 accurately in human CSF. Clinical validation revealed lower levels of Abeta40 in FTLD patients. This finding opens new possibilities for early and differential diagnosis of dementia.

A worldwide multicentre comparison of assays for cerebrospinal fluid biomarkers in Alzheimer's disease

BACKGROUND

Different cerebrospinal fluid (CSF) amyloid-beta 1-42 (Abeta(1-42)), total Tau (Tau) and Tau phosphorylated at threonine 181 (P-Tau) levels are reported, but currently there is a lack of quality control programmes. The aim of this study was to compare the measurements of these CSF biomarkers, between and within centres.

METHODS

Three CSF-pool samples were distributed to 13 laboratories in 2004 and the same samples were again distributed to 18 laboratories in 2008. In 2004 six laboratories measured Abeta(1-42), Tau and P-Tau and seven laboratories measured one or two of these marker(s) by enzyme-linked immunosorbent assays (ELISAs). In 2008, 12 laboratories measured all three markers, three laboratories measured one or two marker(s) by ELISAs and three laboratories measured the markers by Luminex.

RESULTS

In 2004, the ELISA intercentre coefficients of variance (interCV) were 31%, 21% and 13% for Abeta(1-42), Tau and P-Tau, respectively. These were 37%, 16% and 15%, respectively, in 2008. When we restricted the analysis to the Innotest (N = 13) for Abeta(1-42), lower interCV were calculated (22%). The centres that participated in both years (N = 9) showed interCVs of 21%, 15% and 9% and intra-centre coefficients (intraCV) of variance of 25%,18% and 7% in 2008.

CONCLUSIONS

The highest variability was found for Abeta(1-42). The variabilities for Tau and P-Tau were lower in both years. The centres that participated in both years showed a high intraCV comparable to their interCV, indicating that there is not only a high variation between but also within centres. Besides a uniform standardization of (pre)analytical procedures, the same assay should be used to decrease the inter/intracentre variation.

Engineered antibody intervention strategies for Alzheimer's disease and related dementias by targeting amyloid and toxic oligomers

Most neurodegenerative disorders, such as Alzheimer's (AD), Parkinson's, Huntington's and Creutzfeldt-Jakob disease, are characterised by the accumulation of insoluble filamentous aggregates known as amyloid. These pathologies share common pathways involving protein aggregation which can lead to fibril formation and amyloid plaques. The 4 kDa Abeta peptide (39-43 amino acids) derived from the proteolysis of the amyloid precursor protein is currently a validated target for therapy in AD. Both active and passive immunisation studies against Abeta are being trialled as potential AD therapeutic approaches. In this study, we have characterised engineered antibody fragments derived from the monoclonal antibody, WO-2 which recognises an epitope in the N-terminal region of Abeta (amino acids 2-8 of Abeta). A chimeric recombinant Fab (rFab) and single chain fragments (scFvs) of WO-2 were constructed and expressed in Escherichia coli. Rationally designed mutants to improve the stability of antibody fragments were also constructed. All antibody formats retained high affinity (K(D) approximately 8 x 10(-9) M) for the Abeta peptide, comparable with the intact parental IgG as measured by surface plasmon resonance. Likewise, all engineered fragments were able to: (i) prevent amyloid fibrillisation, (ii) disaggregate preformed Abeta(1-42) fibrils and (iii) inhibit Abeta(1-42) oligomer-mediated neurotoxicity in vitro as efficiently as the whole IgG molecule. These data indicate that the WO-2 antibody and its fragments have immunotherapeutic potential. The perceived advantages of using small Fab and scFv engineered antibody formats which lack the effector function include more efficient passage across the blood-brain barrier and minimising the risk of triggering inflammatory side reactions. Hence, these recombinant antibody fragments represent attractive candidates and safer formulations of passive immunotherapy for AD.

Independent inhibition of Alzheimer disease beta- and gamma-secretase cleavage by lowered cholesterol levels

The major molecular risk factor for Alzheimer disease so far identified is the amyloidogenic peptide Abeta(42). In addition, growing evidence suggests a role of cholesterol in Alzheimer disease pathology and Abeta generation. However, the cellular mechanism of lipid-dependent Abeta production remains unclear. Here we describe that the two enzymatic activities responsible for Abeta production, beta-secretase and gamma-secretase, are inhibited in parallel by cholesterol reduction. Importantly, our data indicate that cholesterol depletion within the cellular context inhibits both secretases additively and independently from each other. This is unexpected because the beta-secretase beta-site amyloid precursor protein cleaving enzyme and the presenilin-containing gamma-secretase complex are structurally different from each other, and these enzymes are apparently located in different subcellular compartments. The parallel and additive inhibition has obvious consequences for therapeutic research and may indicate an intrinsic cross-talk between Alzheimer disease-related amyloid precursor protein processing, amyloid precursor protein function, and lipid biology.

Analysis of Abeta interactions using ProteinChip technology

Abeta peptides are now acknowledged to play a central role in the pathogenesis of Alzheimer's disease. Their generation results from the sequential cleavage of amyloid precursor protein by beta and gamma secretases. The resulting peptide fragments impart toxicity via their ability to form soluble oligomers and bind to cell membranes. In this chapter we describe the use of ProteinChip technology to study the physicochemical behaviour of Abeta and its mechanisms of toxicity. These include analyzing (1) Abeta processing and quantitation of peptide fragments, (2) Abeta aggregation and the quantitation of oligomers, and (3) Abeta-lipid interactions.

Intraneuronal amyloid-β plays a role in mediating the synergistic pathological effects of apoE4 and environmental stimulation

The allele E4 of apolipoprotein E4 (apoE4), which is the most prevalent genetic risk factor of Alzheimer's disease (AD), inhibits synaptogenesis and neurogenesis and stimulates apoptosis in brains of apoE4 transgenic mice that have been exposed to an enriched environment. In the present study, we investigated the hypothesis that the brain activity-dependent impairments in neuronal plasticity, induced by apoE4, are mediated via the amyloid cascade. Importantly, we found that exposure of mice transgenic for either apoE4, or the Alzheimer's disease benign allele apoE3, to an enriched environment elevates similarly the hippocampal levels of amyloid-beta peptide (Abeta) and apoE of these mice, but that the degree of aggregation and spatial distribution of Abeta in these mice are markedly affected by the apoE genotype. Accordingly, environmental stimulation triggered the formation of extracellular plaque-like Abeta deposits and the accumulation of intra-neuronal oligomerized Abeta specifically in brains of apoE4 mice. Further experiments revealed that hippocampal dentate gyrus neurons are particularly susceptible to apoE4 and environmental stimulation and that these neurons are specifically enriched in both oligomerized Abeta and apoE. These findings show that the impairments in neuroplasticity which are induced by apoE4 following environmental stimulation are associated with the accumulation of intraneuronal Abeta and suggest that oligomerized Abeta mediates the synergistic pathological effects of apoE4 and environmental stimulation.

Prediction of Alzheimer's disease using the CSF Abeta42/Abeta40 ratio in patients with mild cognitive impairment

Evidence supports an important role for beta-amyloid (Abeta) in the pathogenesis of Alzheimer's disease (AD). Here, we investigate baseline levels of the 40- and 42-amino-acid-long Abeta peptides (Abeta40 and Abeta42) in cerebrospinal fluid (CSF) from a cohort of patients with mild cognitive impairment (MCI, n = 137) in relation to the final diagnosis after 4-6 years of follow-up time. CSF Abeta42 concentration at baseline and the Abeta42/Abeta40 ratio were significantly decreased in the MCI patients who developed AD as compared to cognitively stable MCI patients and MCI patients who developed other forms of dementia (p < 0.001). The baseline levels of Abeta40 were similar in all MCI groups but correlated with change in Mini Mental State Examination scores in converters to AD. The Abeta42/Abeta40 ratio was superior to Abeta42 concentration with regard to identifying incipient AD in MCI (p < 0.05). In conclusion, the data provide further support for the view that amyloid precursor protein metabolism is disturbed in early sporadic AD and points to the usefulness of the Abeta42/Abeta40 ratio as a predictive biomarker for AD.

Humoral immune responses to peptides derived from the beta-amyloid peptide C-terminal sequence

There is a continuing interest in the immunochemical quantification of isoforms of amyloid beta-peptide (Abeta) in body fluids of patients with Alzheimer's disease (AD); however, at present there is no general procedure to produce and test the required antibodies. We examined various methods to generate rabbit anti-Abeta; antibodies that are specific for Abeta(38), Abeta(40) and Abeta(42), and we tested their specificity and sensitivity by ELISA and Western blotting. To produce high-affinity antibodies required repeated inoculations of small doses of peptide conjugates over a period of at least 6 months. Antibodies generated to peptides derived from the Abeta(42) sequence showed some cross-reactivity with Abeta(40), but antibodies generated to Abeta4 peptides did not cross-react with Abeta(42). The shortest peptide capable of generating antibodies of moderate affinity possessed the sequence Met(35)-Ala(42); however, antibodies raised to the peptide Gly(33)-Ala(42) possessed the greatest affinity (K(D) = 1 nM) and specificity for Abeta(42). The latter antibodies were over 50,000-fold more reactive with Abeta(42) than with Abeta(40). They can detect Abeta isoforms in extracts of normal brain, where the peptides are present at levels below one part per billion. Our results provide methods to generate and characterize the specificity and affinity of anti-Abeta antibodies. This information is necessary to develop sensitive and specific immunoassays to quantify Abeta isoforms in brain extracts and in body fluids.

Monoclonal antibodies that target pathological assemblies of Aβ

Amyloid beta (Abeta) immunotherapy for Alzheimer's disease has shown initial success in mouse models of Alzheimer's disease and in human patients. However, because of meningoencephalitis in clinical trials of active vaccination, approaches using therapeutic antibodies may be preferred. As a novel antigen to generate monoclonal antibodies, the current study has used Abeta oligomers (amyloid beta-derived diffusible ligands, ADDLs), pathological assemblies known to accumulate in Alzheimer's disease brain. Clones were selected for the ability to discriminate Alzheimer's disease from control brains in extracts and tissue sections. These antibodies recognized Abeta oligomers and fibrils but not the physiologically prevalent Abeta monomer. Discrimination derived from an epitope found in assemblies of Abeta1-28 and ADDLs but not in other sequences, including Abeta1-40. Immunoneutralization experiments showed that toxicity and attachment of ADDLs to synapses in culture could be prevented. ADDL-induced reactive oxygen species (ROS) generation was also inhibited, establishing this response to be oligomer-dependent. Inhibition occurred whether ADDLs were prepared in vitro or obtained from Alzheimer's disease brain. As conformationally sensitive monoclonal antibodies that selectively immunoneutralize binding and function of pathological Abeta assemblies, these antibodies provide tools by which pathological Abeta assemblies from Alzheimer's disease brain might be isolated and evaluated, as well as offering a valuable prototype for new antibodies useful for Alzheimer's disease therapeutics.

The neurofilament heavy chain (NfH) in the cerebrospinal fluid diagnosis of Alzheimer's disease

BACKGROUND/AIMS

Attempting to improve the cerebrospinal fluid (CSF) diagnosis of Alzheimer's disease (AD), the neurofilament heavy chain isoform, NfH(SMI35) was compared to other CSF markers [total tau, phospho-tau, amyloid beta 1-42 (Abeta42), the ratio of amyloid beta fragments Abeta42/Abeta40 (Abeta ratio)].

METHODS

CSF levels were determined in patients with AD (n = 109), mild cognitive impairment (MCI, n = 25), frontotemporal dementia (n = 15), vascular dementia (VD, n = 41), and controls (n = 58).

RESULTS

CSF NfH(SMI35) was elevated in AD and VD as compared to controls (p < 0.05). Total tau was higher in AD as compared to controls (p < 0.05). CSF phospho-tau was elevated in AD as compared to controls and VD (p < 0.05 each). CSF Abeta42 and Abeta ratios in AD were lower than in MCI and controls (p < 0.05 each).

CONCLUSION

The diagnostic potential of NfH(SMI35) is not superior to that of other CSF markers.

Deposition of mouse amyloid β in human APP/PS1 double and single AD model transgenic mice

The deposition of amyloid beta (Abeta) peptides and neurofibrillary tangles are the two characteristic pathological features of Alzheimer's disease (AD). To investigate the relation between amyloid precursor protein (APP) production, amyloid beta deposition and the type of Abeta in deposits, i.e., human and/or mouse, we performed a histopathological analysis, using mouse and human specific antibodies, of the neocortex and hippocampus in 6, 12 and 19 months old APP/PS1 double and APP and PS1 single transgenic mice. There was a significant correlation between the human amyloid beta deposits and the intrinsic rodent amyloid beta deposits, that is, all plaques contained both human and mouse Abeta, and the diffuse amyloid beta deposits also colocalized human and mouse Abeta. Furthermore, some blood vessels (mainly leptomeningeal vessels) show labeling with human Abeta, and most of these vessels also label with mouse Abeta. Our findings demonstrate that the human amyloid deposits in APP/PS1 transgenic mice are closely associated with mouse Abeta, however, they do not precisely overlap. For instance, the core of plaques consists of primarily human Abeta, whereas the rim of the plaque contains both human and mouse amyloid beta, similarly, human and mouse Abeta are differentially localized in the blood vessel wall. Finally, as early as amyloid beta deposits can be detected, they show the presence of both human and mouse Abeta. Together, these data indicate that mouse Abeta is formed and deposited in significant amounts in the AD mouse brain and that it is deposited together with the human Abeta.

Impact of different saturated fatty acid, polyunsaturated fatty acid and cholesterol containing diets on beta-amyloid accumulation in APP/PS1 transgenic mice

The present study assessed the influence of dietary lipids on accumulation of amyloid beta-peptide (Abeta) in the brain. Seven experimental diets with varying n-6/n-3-ratio, saturated and polyunsaturated fatty acid and cholesterol contents were fed to transgenic APPswe/PS1dE9 mice for 3-4 months beginning at a young adult age (6 months). Hippocampal Abeta levels were determined with ELISA and plaque load by using immunocytochemistry. A typical Western diet with 40% saturated fatty acids and 1% of cholesterol increased, while diets supplemented with docosahexaenoic acid (DHA) decreased Abeta levels compared to regular (soy oil based) diet. DHA diet also decreased the number of activated microglia in hippocampus and increased exploratory activity of transgenic mice, but did not improve their spatial learning in the water maze. The favorable effect of DHA on Abeta production was verified in two different cell lines. Regulation of dietary lipid intake may offer a new tool to reduce the risk of Alzheimer's disease at the population level.

Central nervous system drug development: an integrative biomarker approach toward individualized medicine

Drug development for CNS disorders faces the same formidable hurdles as other therapeutic areas: escalating development costs; novel drug targets with unproven therapeutic potential; and health care systems and regulatory agencies demanding more compelling demonstrations of the value of new drug products. Extensive clinical testing remains the core of registration of new compounds; however, traditional clinical trial methods are falling short in overcoming these development hurdles. The most common CNS disorders targeted for drug treatment are chronic, slowly vitiating processes manifested by highly subjective and context dependent signs and symptoms. With the exception of a few rare familial degenerative disorders, they have ill-defined or undefined pathophysiology. Samples selected for treatment trials using clinical criteria are inevitably heterogeneous, and dependence on traditional endpoints results in early proof-of-concept trials being long and large, with very poor signal to noise. It is no wonder that pharmaceutical and biotechnology companies are looking to biomarkers as an integral part of decision-making process supported by new technologies such as genetics, genomics, proteomics, and imaging as a mean of rationalizing CNS drug development. The present review represent an effort to illustrate the integration of such technologies in drug development supporting the path of individualized medicine.

CSF biomarkers for mild cognitive impairment and early Alzheimer's disease

A correct clinical diagnosis, early in the course of Alzheimer's disease (AD), is of importance given the currently available symptomatic treatment with acetylcholine esterase inhibitors. The development of disease-modifying drugs like beta-sheet breakers or gamma- and beta-secretase inhibitors, emphasizes the need of improved diagnostic accuracy, especially in patients with mild cognitive impairment (MCI) that have incipient AD. Therefore, diagnostic markers in the cerebrospinal fluid (CSF) have become a rapidly growing research field. Three cerebrospinal fluid biomarkers (the 42 amino acid form of beta-amyloid (A beta), total tau, and phospho tau) have been evaluated in numerous scientific papers. These CSF markers have high sensitivity to differentiate early and incipient AD from normal aging, depression, alcohol dementia and Parkinson's disease, but lower specificity against other dementias, such as frontotemporal and Lewy body dementia. If these biomarkers are used in combination with a careful medical history, clinical examination, standard laboratory tests and imaging techniques of the brain, the diagnostic accuracy may be appropriate for the clinical evaluation of MCI cases.

Effects of processing and storage conditions on amyloid beta (1-42) and tau concentrations in cerebrospinal fluid: implications for use in clinical practice

BACKGROUND

Reported concentrations of amyloid beta (1-42) (A beta 42) and tau in cerebrospinal fluid (CSF) differ among reports. We investigated the effects of storage temperature, repeated freeze/thaw cycles, and centrifugation on the concentrations of A beta 42 and tau in CSF.

METHODS

Stability of samples stored at -80 degrees C was determined by use of an accelerated stability testing protocol according to the Arrhenius equation. A beta 42 and tau concentrations were measured in CSF samples stored at 4, 18, 37, and -80 degrees C. Relative CSF concentrations (%) of the biomarkers after one freeze/thaw cycle were compared with those after two, three, four, five, and six freeze/thaw cycles. In addition, relative A beta 42 and tau concentrations in samples not centrifuged were compared with samples centrifuged after 1, 4, 48, and 72 h.

RESULTS

A beta 42 and tau concentrations were stable in CSF when stored for a long period at -80 degrees C. CSF A beta 42 decreased by 20% during the first 2 days at 4, 18, and 37 degrees C compared with -80 degrees C. CSF tau decreased after storage for 12 days at 37 degrees C. After three freeze/thaw cycles, CSF A beta 42 decreased 20%. CSF tau was stable during six freeze/thaw cycles. Centrifugation did not influence the biomarker concentrations.

CONCLUSIONS

Repeated freeze/thaw cycles and storage at 4, 18, and 37 degrees C influence the quantitative result of the A beta 42 test. Preferably, samples should be stored at -80 degrees C immediately after collection.

Neurochemical diagnosis of Alzheimer's dementia by CSF Abeta42, Abeta42/Abeta40 ratio and total tau

Cerebrospinal fluid (CSF) concentrations of amyloid beta peptides ending at positions 42 and 40 (Abeta42 and Abeta40, respectively), and total tau (tTau) protein were measured by ELISA in order to compare their accuracy in discriminating patients with Alzheimer's disease (AD, n = 22), non-Alzheimer dementia (nAD, n = 11) and control subjects (CON, n=35). As compared to the other groups, the concentrations of Abeta42 and tTau were decreased (P<0.001) and increased (P<0.001) in AD, respectively, while Abeta40 did not differ significantly among the groups. Receiver operating characteristic (ROC) analysis was performed to define cut-off values for maximized sensitivity and specificity. For all groups compared the Abeta peptide ratio 42/40 classified more patients correctly, as compared to the concentration of Abeta42 alone: AD versus controls, 94 and 86.7%; AD versus nAD, 90 and 85% and AD versus nAD plus controls, 90.8 and 87%, respectively. The percentage of correctly classified patients was further improved when the Abeta ratio was combined with the analysis of the tTau concentration. Presence of the apolipoprotein E 4 allele, age or degree of mental disability did not significantly influence the parameters studied.

Amyloid beta peptides in cerebrospinal fluid as profiled with surface enhanced laser desorption/ionization time-of-flight mass spectrometry: evidence of novel biomarkers in Alzheimer's disease

BACKGROUND

The advent of new therapeutic avenues for Alzheimer's disease (AD) calls for an improved early and differential diagnosis.

METHODS

With surface enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS), cerebrospinal fluid from patients with AD (n = 10) and nondemented control subjects (n = 9) was studied.

RESULTS

Molecular mass signals were observed corresponding to three novel amyloid beta (Abeta) peptides that have not previously been described, in addition to those previously known, with molecular masses of 4525.1 d, 4846.8 d, and 7755.8 d. The signal-to-noise ratios (S/NR) of Abeta(4525.1) and Abeta(7758.8+2H) were significantly decreased in AD [Abeta(4525.1): median 2.2 and 4.3 in AD and control subjects, respectively, p <.01; Abeta(7758.8+2H): median 1.0 and 14.0 in AD and control subjects, respectively, p <.01], whereas the S/NR of Abeta(4846.8) was significantly increased in AD (median 3.6 and 2.5 in AD and control subjects, respectively, p <.05). The S/NR of two known AD biomarkers, Abeta1-42 and Abeta1-40, expectedly turned out to be significantly decreased (p <.01) and unaltered in AD, respectively. A moderate and highly significant correlation was observed between S/NR of Abeta1-42 and Abeta42 concentration as measured with enzyme-linked immunosorbent assay (R =.67, p <.01).

CONCLUSIONS

We report evidence of three novel amyloid beta peptides that might play an important role in the diagnosis and pathophysiology of Alzheimer's disease.

CSF markers for Alzheimer's disease: total tau, phospho-tau and Abeta42

Today we have the first therapeutic compounds for treatment of Alzheimer's disease (AD) e.g. acetylcholine esterase inhibitors and in the near future we may expect new compounds such as gamma- and beta-secretase inhibitors. This has demanded increased accuracy in the diagnosis of AD and thus, among other possible approaches, diagnostic markers in the cerebrospinal fluid (CSF) have become a rapidly growing research field. Especially early in the course of the disease, when correct diagnosis is most difficult, such biomarkers would be especially valuable as one might expect the compounds to have the greatest potential of being effective. Two of the defining lesions in AD brains are senile plaques and neurofibrillary tangles with beta-amyloid (Abeta) and tau proteins as the main components respectively. Abeta and tau proteins are secreted to body fluids including plasma and cerebrospinal fluid (CSF). In this paper we review CSF markers for AD, with focus on their role in the clinical diagnosis. Reduced CSF levels of the 42 amino acid form of Abeta (Abeta42) and increased CSF levels of total tau (T-tau) in AD have been found in numerous studies, with high sensitivity figures. However, the specificity against other dementias is lower. The addition of phospho-tau (P-tau) seems to increase the specificity, since normal levels are found in other dementias and in cerebrovascular disease. An increasing number of studies suggests that these CSF markers perform well enough to have a role in the clinical work-up of patients with dementia if used together. We stress that the CSF markers should be combined with the clinical information and brain-imaging techniques.

Clinical findings in nondemented mutation carriers predisposed to Alzheimer's disease: a model of mild cognitive impairment

Individuals carrying a mutation associated with Alzheimer's disease (AD) may serve as a model of mild cognitive impairment (MCI). Nondemented individuals from these families can be subdivided into asymptomatic and symptomatic groups. Four families were studied. Two families are associated with APP mutations (KN670/671ML, E693G) and two with PS1 mutation (M146V, H163Y). Clinical symptoms, level of global cognitive functioning as evaluated by Mini-Mental State Examination, neuropsychological test results, neuroradiological examinations (magnetic resonance imaging (MRI) and single-photon emission tomography (SPECT)), as well as cerebrospinal fluid (CSF) measurements of tau and beta-amyloid are reported. Nondemented mutation carriers did not report any symptoms indicating cognitive decline. In addition, no clinical signs of dementia or marked cognitive impairment in neuropsychological tests were found. A reduction of temporal blood flow with SPECT was indicated in 5/13 nondemented mutation carriers. Two of these 13 individuals had moderate hyperintensities in deep white matter as observed on MRI. CSF measurements of A beta 42/43 were inconclusive because of large biological variation. A nonsignificant elevation of tau was detected in mutation carriers. In conclusion, clinical examinations of relatively young individuals carrying an AD mutation did not reveal any marked abnormalities before the clinical onset of dementia.

Fimbria-fornix lesion does not affect APP levels and amyloid deposition in the hippocampus of APP+PS1 double transgenic mice

The deposition of amyloid beta peptides (Abeta) and cholinergic dysfunction are two characteristic features of Alzheimer's disease. Several studies have suggested that a compromised cholinergic transmission can increase the amount of amyloid precursor protein (APP) in the denervated cortex (or hippocampus); however, whether this will increase Abeta production is unknown. To investigate the relation between cholinergic neurotransmission and APP metabolism, and the possible role of cholinergic dysfunction in the development of amyloid neuropathology, we lesioned the fimbria-fornix pathway in APP+PS1 double transgenic mice, at 5 and 7 months of age. Three months and 11 months postlesion, the mice were sacrificed for biochemical and histopathological analyses. The fimbria-fornix transection resulted in a substantial depletion of cholinergic markers in the hippocampus at both time points. Three months postlesion, hippocampal APP and Abeta levels were not significantly changed. At 11 months postlesion, the fimbria-fornix lesion did not result in an alteration in either the hippocampal Abeta levels or the extent of Abeta deposition, as assessed by amyloid plaque counts and image analysis of Abeta load in the 18-month-old APP+PS1 mice. Our findings indicate that APP metabolism in mice may be dissociated from cholinergic neurotransmission rather than related as previously suggested in other mammalian species.